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Boron carbon oxynitride (BCNO) and boron carbon nitrogen (BCN) nanocompounds are successfully synthesized by a solid state sintering method using boric acid, urea and dextrose as the sources of B, N and C respectively under inert atmosphere. X-ray diffraction (XRD) and infrared spectroscopy (FTIR) analysis show that nanomaterials are synthesized at the high temperature range of 1350 °C. Sufficient amount of oxygen impurities are present in the sample, which is manifested in their photoluminescence spectra. Increase in temperature to 1350 °C under N2 atmosphere causes elimination of significant amount of O-species from the system. The presence of ample amount of carbon in the system results in the formation of high amount of polycrystalline h-BCN with minor amount of h-BN. However, some residual oxygen in the sample, which is detected in the FTIR study, leads to the formation of BCNO compound. These semiconductor BCNO compounds act as the potential luminescence centers for the blue-green emissions of the particles. Thus, these materials may find potential application as a phosphor material in various opto-electronic devices.

In this study, the effect of a single overload on the fatigue life of cracked aluminum 2024-T3 alloy repaired with a bonded composite patch were studied. Special consideration was given to the load history, sequence of the bonded patch repair and the overload application (repair-overload and overload-repair). The two cases were compared to a reference case involving a single overload on unrepaired specimen. Fatigue tests were performed on V-notched repaired and unrepaired specimens naturally pre-cracked under constant amplitude loading. Fractographic analysis on the failed specimens was carried out to analyze the obtained fatigue results. It was found that when the crack is repaired before the overload application, the retardation effect due to the overload is attenuated by the patch. Nonetheless, when the patch precedes the overload, very high fatigue life extension of about 38.9 times is observed due to a cumulative retardation effect of the two events (patching and overload).

Under real working conditions, structures are subjected to variable and peak loads. It is well known that cracks growth rate is load history dependent. Overloads generate crack growth retardation while underloads produce acceleration in crack growth. The effect of load history on patch repair is not covered so far. In this work, we investigated experimentally, how a single overload peak affects the performance of a bonded composite patch repair in cracked Al 2024-T3 and 7075-T6 samples fatigued under a cyclic loading. We studied the effect of three overload peaks; 9, 12 and 14 kN, applied just before and soon after the bonded composite repair. The fatigue lives and retardation cycle numbers exhibited that subjecting the test sample to overload before the repair will cause more retardation of the crack growth, while the reverse will result in less retardation, yet still better than that subjected to an overload alone. We carried out SEM observations to analyse the fractographs of failed specimens subjected to overloads and observed mixed mode fracture type.

The mechanical response of a servo-hydraulic testing system is affected by the stiffness of test specimens. An adaptive controller helps in auto-tuning the system by setting the optimal proportional-integral-derivative values for the subsequent test as the stiffness changes. This paper presents the effect of auto-tuning of various channels on the flow response of several commercial Al and Mg alloys and a mild steel. Strain-controlled monotonic tensile tests were performed at a given strain rate of 1 &times, 10&minus, 4 s&minus, 1 after auto-tuning of position, load, and strain channels in different combinations. Serrated flow or Portevin&ndash, Le Chatelier effect was observed in the Al alloys after auto-tuning of either position channel only or position and load channels. However, the serrations of Al alloys were shielded after further auto-tuning of strain channel. The stress-strain curves of Mg alloys and mild steel were observed to be basically free of serrations under any combinations of auto-tuning, which confirms that the serrated flow is a property of specific materials rather than a machine system noise.

The purpose of this investigation was to study the low-cycle fatigue (LCF) behavior of a newly developed high-pressure die-cast (HPDC) Al-5.5Mg-2.5Si-0.6Mn-0.2Fe (AlMgSiMnFe) alloy. The effect of heat-treatment in comparison with its as-cast counterpart was also identified. The layered (&alpha, Al + Mg2Si) eutectic structure plus a small amount of Al8(Fe,Mn)2Si phase in the as-cast condition became an in-situ Mg2Si particulate-reinforced aluminum composite with spherical Mg2Si particles uniformly distributed in the &alpha, Al matrix after heat treatment. Due to the spheroidization of intermetallic phases including both Mg2Si and Al8(Fe,Mn)2Si, the ductility and hardening capacity increased while the yield stress (YS) and ultimate tensile strength (UTS) decreased. Portevin&ndash, Le Chatelier effect (or serrated flow) was observed in both tensile stress&ndash, strain curves and initial hysteresis loops during cyclic deformation because of dynamic strain aging caused by strong dislocation&ndash, precipitate interactions. The alloy exhibited cyclic hardening in both as-cast and heat-treated conditions when the applied total strain amplitude was above 0.4%, below which cyclic stabilization was sustained. The heat-treated alloy displayed a larger plastic strain amplitude and a lower stress amplitude at a given total strain amplitude, demonstrating a superior fatigue resistance in the LCF regime. A simple equation based on the stress amplitude of the first and mid-life cycles ((&Delta, &sigma, /2)first, (&Delta, /2)mid) was proposed to characterize the degree of cyclic hardening/softening (D): D=&plusmn, (&Delta, /2)mid&nbsp, &minus, &nbsp, /2)first(&Delta, /2)first, where the positive sign &ldquo, +&rdquo, represents cyclic hardening and the negative sign &ldquo, &ldquo, reflects cyclic softening.

The aim of this investigation was to assess the corrosion behavior of gray cast iron (GCI) alloyed with copper. Alloyed GCI specimens were austempered isothermally at varying temperatures. After austenitizing at 927 &deg, C, the samples were austempered at different temperatures ranging from 260 to 385 &deg, C with an interval of 25 &deg, C for 60 minutes. As a result, these samples developed an ausferrite matrix with different percentages of austenite. The resulting microstructures were evaluated and characterized by optical microscope (OM), scanning electron microscope (SEM), and X-ray diffraction (XRD). The corrosion characteristics were determined using potentiodynamic polarization tests and electrochemical impedance spectroscopy (EIS) of these samples. These tests were carried out in a medium of 0.5 M H2SO4 and 3.5% NaCl solution. It was observed from the potentiodynamic polarization results that with increasing austempering temperature, the corrosion rate decreased. All results of the EIS were in accordance with a constant phase element (CPE) model. It was found that with an increase in austempering temperature, the polarization resistance (Rp) increased. The austenite content was also found to influence the corrosion behavior of the austempered gray cast iron (AGCI).

In the recent years, metal foams have become promising candidate materials in the engineering sector owing to their light weight and excellent energy absorption properties. Friction stir processing (FSP) has emerged as a cost-effective route to fabricate metal foam precursors from bulk substrates. Although the short processing time in FSP is able to provide high productivity, the cost of the foaming agent, TiH2 in the case of aluminum foams is still high. This paper introduces flame heating to achieve localized foaming of aluminum alloy AA5754 to explore the possibility of using magnesium carbonate as a foaming agent stirred using multi-pass FSP. A specially designed slot based strategy using two plates arranged in lap configuration is devised to stir the foaming agent and understand the material movement after each subsequent pass. Microscopy techniques were carried out to evaluate the distribution of the foaming agent after each pass and the resulting microstructure of the processed plates as well as the morphology of the foamed sample. EDX results showed higher Mg and O content around the pore walls.

The aim of this study is to find out the microstructure, hardness, and corrosion resistance of Pb-5%Sb spine alloy. The alloy has been produced by high pressure die casting (HPDC), medium pressure die casting (AS) and low pressure die casting (GS) methods, respectively. The microstructure was characterized by using optical microscopy and scanning electron microscopy (SEM). The hardness was also reported. The corrosion resistance of the spines in 0.5M H2SO4 solution has been analyzed by measuring the weight loss, impedance spectroscopy and the potentiodynamic polarization techniques. It has been found that the spine produced by HPDC has defect-free fine grain structure resulting improvement in hardness and excellent corrosion resistance.